“Discipline” is commonly used to denote particular areas of knowledge, research and education. Yet, the concept is often not very well defined or even explicitly discussed when used in knowledge organisation and related fields. The aim of this article is to encourage and facilitate further reflections on academic disciplines, while at the same time offering insights on how this elusive concept might be understood. An overarching argument is that “discipline” should foremost be understood in relation to institutional and organisational features, and this is what distinguishes it from related terms such as, field, domain or topic. The etymology and history of the concept are reviewed along with a discussion of attempts to define and conceptualise disciplines. Insights are offered on how disciplines might be studied. Regardless of our views of disciplines, either as inherently out-dated constructs or as important features of a well-functioning academia, it is concluded that further precision or care in explicating the concept is needed.